Report errors and warnings for hiding elements, issue 572.

compiler/lib/implementation/string.dart

Index: compiler/lib/implementation/string.dart
diff --git a/compiler/lib/implementation/string.dart b/compiler/lib/implementation/string.dart
index d227e8803b1cec2db5bfd22a30129c85e60568cd..14bd63ff91aa11ed31c36b43d834ec10a9b27773 100644
--- a/compiler/lib/implementation/string.dart
+++ b/compiler/lib/implementation/string.dart
@@ -214,16 +214,16 @@ class _StringMatch implements Match {
   String operator[](int g) => group(g);
   int groupCount() => 0;
 
-  String group(int group) {
-    if (group != 0) {
-      throw new IndexOutOfRangeException(group);
+  String group(int group_) {
+    if (group_ != 0) {
+      throw new IndexOutOfRangeException(group_);
     }
     return pattern;
   }
 
-  List<String> groups(List<int> groups) {
+  List<String> groups(List<int> groups_) {
     List<String> result = new List<String>();
-    for (int g in groups) {
+    for (int g in groups_) {
       result.add(group(g));
     }
     return result;